1. Field of the Invention
The present invention concerns devices that enable underwater vehicles or equipment such as sonars, towed behind ships, to be kept submerged at a substantially constant depth. Such devices are known in the prior art as hydrodynamic depressers.
2. Description of the Prior Art
As shown in FIG. 1, it is common practice to tow an underwater vehicle 103, called a fish, behind a ship 101. This vehicle 103 is pulled by means of a cable 104. This fish has a variety of instrument systems, for example a sonar designed to map the ocean bed. This fish has to be maintained at an submersion depth H which is sufficient, inter alia, to get rid of the effects of surface noises to the maximum extent. It is also very desirable for this submersion depth to be kept as constant as possible.
It is quite clear that, because of the drag shown by the fish and also by the cable, the faster the ship goes, the more will the fish tend to rise towards the surface.
To prevent this, it is common to use a depresser 105 with a shape designed so that its head resistance tends, on the contrary, to make it plunge, in dragging along the cable to which it is hooked and the fish hooked to the cable. The dimensions of this whole unit are designed so that the vertical forces exerted on the fish and on the depresser cancel each other, preferably in the widest possible range of speeds.
Essentially two types of depressers are known:
A first model, shown in FIG. 2, comprises a set of flaps 202 held by two vertical panels 203. These panels are hooked to four suspenders 201, the relative lengths of which enable the flaps to be maintained with an angle of incidence enabling the necessary downward thrust to be obtained. A depresser such as this is relatively compact, but works accurately only at low speeds. Moreover, the drag forces due to the vertical panels 203 are relatively great, without any advantages being provided by these panels.
A second model, manufactured notably by the firm ENDECO Incorporated at MARION (Massachussets), U.S., is formed by a delta wing that has a fairly accentuated negative dihedron and is provided with a vertical aileron. This wing is hooked on at a single anchoring point located slightly in front of the center of the wing. The central aileron, which is necessary to ensure the rolling stability, itself also has a high level of unwanted roll. Besides, the pitching stability of such devices is relatively low.